How many liters are in one imperial gallon?

One imperial gallon is equivalent to approximately 4.54609 liters. In practical terms, it is often rounded to 4.5 liters for ease of understanding and calculation. The imperial gallon is used primarily in the United Kingdom and some Commonwealth countries, differing significantly from the US customary gallon which contains about 3.785 liters. Understanding this conversion is essential for plumbing practices that may require precise water measurements, such as in the installation or maintenance of plumbing systems.